Hydraulic cylinder actuator



Feb. 15, 1966 s A R 3,234,853

HYDRAULIC CYLINDER ACTUATOR Filed 0011. 18, 1963 INVENTOR JOSEPH S. ABERBY 7 4m ATTORNEY United States Patent Ofilice 3,234,853 Patented Feb.15, 1966 3,234,853 HYDRAULIC CYLINDER ACTUATOR Joseph S. Aber,Philadelphia, Pa. (439 Argyle Road, Drexel Hill, Pa.) Filed Get. 18,1963, Ser. No. 317,164 1 Claim. (Cl. 914) This invention relates to anactuator for a hydraulic cylinder. More particularly, it relates toactuating means for a hydraulic cylinder in which gas pressure is usedin combination with hydraulic fluid.

In certain types of hydraulically actuated cylinders, a reservoir ofhydraulic fluid is provided with access to the cylinder on each side ofthe piston within the cylinder. A differential in the gas pressureapplied to the surfaces of the fluid in the cylinders results in anunbalanced force on the opposing faces of the piston, and the cylinderis thus actuated. Accurate positioning of the piston, and carefullycontrolled movement of it are desirable in certain applications. In manyapplications, it is important that the position and movement of thepiston be held to close tolerances, and that its movement be highlyresponsive to applied control.

Typically, the hydraulic fluid is oil and the gas is air: the terms oiland air are used throughout this specification as terms of convenience,but it is understood that all gases and hydraulic fluids known orsuitable for the use in such hydraulic systems are contemplated withinthe scope of the invention.

A seemingly straightforward system in practice presents somecomplications that adversely affect its desirable characteristics.Sudden high pressure bursts of air impinge on the exposed surface of theoil in a reservoir and it has been found that there is a tendency toentrap air bubbles in the oil, in a manner explained below. Thiscondition reduces the sensitivity of the system. It has also been foundthat when it is desired to hold the piston at a stable position byadmitting equal air pressures to each reservoir, there may still be atendency for the piston to creep because of differentials in theeffective pressure on the surface of the oil in the two reservoirs dueto differences in the characteristics (such as length) of the linesthrough which the air is supplied. Expedients have been practiced towardthe end of reducing or eliminating these problems, and the presentinvention is an improvement over other such expedients.

Prior means to prevent the entrapment of air in the oil are shown forexample in United States Patents 2,683,- 463 and 3,053,233.

It is an object of this invention to provide a hydraulic cylinderactuator.

It is another object of this invention to provide actuating means for anair oil hydraulic cylinder system.

It is yet another object of this invention to provide an air-oilreservoir system adapted for use with a hydraulic cylinder, in whichmeans are provided to prevent churning of the air and oil, and to reduceunwanted pressure differentials.

It is yet another object of this invention to provide means in ahydraulic cylinder oil reservoir to distribute the flow of incoming gasso as to avoid mixing with the oil.

Other aims and objects of this invention are made apparent in thefollowing specification and claim.

The invention is best understood in connection with the drawing. Thedrawing is a schematized cross-sectional elevational View of a hydrauliccylinder and its actuating system.

A conventional hydraulic cylinder generally designated 50 is shown. Thiscylinder 50 is provided with a piston 53 to which is afiixed a pistonrod 54. The piston is free to move axially within the cylinder 50 in theordinary way. Hydraulic fluid, generally oil, 60, is provided inside thecylinder 50 on both sides of piston 53. Oil lines 52 and 51 open intothe cylinder on opposite sides of piston 53.

The actuator is generally designated 10. It comprises a base 49 and atop 30. These elements are preferably made of machined metal stock, suchas brass, and may typically be rectangular blocks of metal, machined orotherwise fashioned to provide recesses and passages therethrough asindicated in the drawing. It is understood that the actuating means,which constitutes the subject of this invention, is illustrated as muchlarger thanthe hydraulic cylinder, which is included in the drawing onlyto show a complete system. In actuality, the scale of the cylinder andactuating means might be reversed.

A pair of reservoir cylinders 34 and 35 are provided between top andbase at). As shown, these hollow cylinders may be mounted between thetop and the base by being fitted into circular grooves milled orotherwise formed in the facing surfaces of the top and base, respectively. Thus, a reservoir cylinder together with its closed top andbottom formed by part of the top 30 and base 40, respectively, may bedescribed as a reservoir. It is understood that tight seals are providedat all joints and the shape of the reservoir is not critical to theinvention. The exact dimensions of the reservoirs are not critical tothe invention, but the typical field of application of this inventionnormally lies in reservoirs whose reservoir cylinders have diameters ofone-inch or more, with the other dimensions of the reservoir typicallyin somewhat the same proportions shown in the drawing, although notnecessarily so. The reservoir cylinders 34 and 35 may be made of metal,or may be made of transparent plastic or glass. There is an advantage inproviding the pair of cylinders of transparent material when they aremounted in the close side-by-side relationship on a common base asillustrated in the preferred embodiment shown. The advantage is that thedifierential in oil levels between the two cylinders is immediately andeasiy visible to the eye of the operator. It is then apparent that thisdifferential is an index to the position of the cylinder. The reservoircylinders 34 and 35 may be provided with etched, engraved or othermarkings to provide index marks so that levels may be readquantitatively. Alternatively, linear measuring means may be provided toquantitatively measure the difference between the levels. Such a meansincludes a simple ruler with provision for raising or lowering itbetween the two reservoirs. It is also apparent, if the level of the oil64 in each cylinder is set so as to be the same when the piston 53 is insome central or standard position, that an immediate quantitative orqualitative visual indication is given as to what side of the standardposition the piston 53 as at any moment, and how far it is displaced.Thus, in the drawing, the oil 60 in reservoir cylinder 34 stands higherthan in cylinder 35, and this corresponds to a displacement of piston 53toward the left of hydraulic cylinder 50.

The oil lines 51 and 52 communicate respectively to reservoir cylinders34 and 35 through the respective bores A and 4613 through base 40.

Air lines 25 and 24 communicate through certain connecting meansdescribed below respectively to reservoir cylinders 34 and 35. Apreferred form of the communicating means is illustrated. Air bores 30Aand 3B are provided in top 3% to respectively receive air lines 25 and24 as shown. These air bores may be horizontal drilled or otherwiseformed in the top 30. Air bore 30A opens to J-tube 32 and air bore 30 Bopens to I-tube 33. J-tube 32 is a pipe or line curved as shown, andfirmly fitted into a bore provided to receive it in top 30, andcommunicating with the inner end of air bore 30A. The J-tube has a longleg which flts into top 30, and a short leg which terminates below thelower surface of top 30. Preferably a ISO-degree turn is provided in thetube. The end of the tube maybe and preferably is flared outwardly asshown. J-tube 33 is described exactly as is J-tube 32, except that inthe preferred embodiment shown, in their mounted positions, tubes 32 and33 have their handedness reversed. In each J-tube, the center of theopen flared end is preferably coaxial with the center line of thecorresponding reservoir cylinder.

An air valve of conventional structure is provided to selectivelyconnect air line to air supply line 26 and air line 24 to air supplyline 23 in one position, and air line 25 to air supply line 23 and airline to air supply line 26 in a second position. The second position isillustrated by the phantom lines in air valve 20. The air valve 20comprises a shell 22 having bores 22A, 22B, 22C, and 22D, therein, whichrespectively receive the lines 25, 26, 24, and 23. A core 21 in valve 20contains curved channels 21B and 21A which can selectively connect airlines to air supply lines as has been described above when the core 21is rotated within shell 22. Other means, not shown, may be provided toregulate the pressure available.

The reservoir cylinders 34 and 35 are mounted close together on a singlebase and underneath a single top to form a single balanced unit. The airvalve 20 is provided close to the actuator unit 10 and the lines 24 and25 are of equal length. The oil lines 51 and 52 are also of equallength, and in general, the structure is such that the total paths tothe opposite sides of piston 53 are kept as short and as equal aspossible. It has been found that differences in the pressure transmittedto the opposite sides of piston 53 due to differences in frictional linedrops can have a significant effect. By thus providing a unitary compactbalanced and short line actuator 10, the possibility of imbalance in thepressure ultimately applied against the opposite faces of piston 53 isreduced. This balanced ultimate pressure is desirable where a stablecondition is desired. Thus, in addition to the visual check advantagesof providing a unitary actuator 10, there is the advantage of a moreeasiy produced stable condition.

In use, systems of the type herein described, where operating pressuresare typically of the order of between and pounds per square inch, thereis a sudden burst of air admitted to a reservoir. This sudden bursttends to impinge on the exposed surface of the oil 60 and tends to churnor mix. As has been explained above, this is undesirable when precisioncontrol is required. Various expedients have been known to minimize thischurning effect. The .T-tube structure herein disclosed has been foundto have less tendency to churn or mix than hitherto known expedients.

It is desirable to avoid any direct blast of air from the air lines onthe surface of oil 60, and also to have the admitted air act on theexposed oil surface 60 as evenly as possible over the entire surface. Acompletely even application of impinging air pressure over the entiresurface is the ultimate desirable condition in avoiding churning. Theherein dsclosed structure is the closest approach yet known to thiscondition. The direct blast of air coming through the ]-tube strikes theundersurface of top 30, rather than being directed at or near thesurface of the oil 60. The passage of the air through the curve in theJ-tube is believed to impart a slight swirling motion to the air whichhelps in the distribution.

The blast of air spreads over the undersurface, and the pressure tendsto be uniformly exerted downwardly as if directed from an outlet havingthe same diameter as the reservoir itself. Any nozzle effect, which ishighly undesirable, is here almost completely eliminated. In hithertoknown expedients, the effective opening from which the air has come hasbeen smaller in relation to the exposed surface of the oil than isavailable in the herein disclosed structure, and this smaller effectiveopening has been found to result in a nozzle effect and consequent blastto at least some degree.

Typically, one air supply line may be connected to a supply of highpressure air, and the other line exhausts to atmosphere. The usefulpressure difierential is that between the air supply and atmosphericpressure. Valve 20 may typically have selective positions as follows:air line 24 to pressure, line 25 to exhaust; line 24 to exhaust, line 25to pressure; lines 24 and 25 both closed; and lines 24- and 25 both toexhaust. The rate of response of the hydraulic cylinder may be regulatedby an oil flow control valve in line 51 or 52 (not shown) as is known inthe art. When both air lines are closed, there is no creep of the pistoneven though there is a difference between the effective areas on eachside of the piston.

The scope of this invention is to be determined by the appended claimand is not to be limited by the foregoing description and drawing whichare intended to be illustrative.

I claim:

An actuation control means for a gas-hydraulic fluid system comprising asingle base, a pair of reservoir cylinders mounted close together onsaid base, a single top covering both of said pair of reservoircylinders, said reservoir cylinders being made of transparent material,oil lines of equal length and configuration leading from the bottom ofeach of said reservoir cylinders to opposite ends of said hydrauliccylinder, an air valve, air lines of equal length and configurationleading from said air valve to the top of each of said reservoircylinders, said air lines communicating to said reservoir cylinders bymeans of air bores in said top, each of said air bores being connectedto a l-tube, each of said J-tubes having a long leg connected to saidair bore and extending downwardly into said reservoir cylinder, a curvedsection connected to said long leg and having a curve of substantially-degrees, a short leg connected to said curved section and having anopen flared end pointing upwardly toward and closely spaced from saidtop, the center of said open end being substantially coincident with thecenter of said reservoir cylinder.

References Cited by the Examiner UNITED STATES PATENTS 375,761 1/1888McKim 137-209 666,156 1/1901 Ridgway 91-4 986,143 3/1911 Crawford137-209 1,147,436 7/1915 Ragonnet 91-4 1,314,153 8/1919 Schneider 91-42,151,998 3/1939 Stelzer 91-4 2,638,748 5/1953 Miller 60-546 2,661,84712/1953 Buettner 60-54.6 2,849,987 9/1958 Shafer 91-4 2.940.518 6/1960Lawler et al 158-501 3,069,847 12/1962 Vest 60-3966 SAMUEL LEVINE,Primary Examiner.

FRED E. ENGELTHALER, Examiner,

